1. Field of the Invention
The present invention relates to methods of manufacturing SOI substrates, semiconductor devices formed using the SOI substrates, and methods of manufacturing the semiconductor devices. It is to be noted that “semiconductor device” in the present specification refers to general devices that can function by use of semiconductor characteristics.
2. Description of the Related Art
A variety of research related to silicon on insulator (SOI) technology is being conducted because integrated circuits that are fabricated using SOI substrates formed of a single-crystal silicon film over an insulating surface have advantages that cannot be obtained with integrated circuits that are fabricated using bulk silicon substrates.
For SOI technology, for example, separation by implanted oxygen (SIMOX) technology by which oxygen is implanted in a single-crystal silicon substrate by ion implantation to form a buried oxide layer; bonding SOI technology by which two silicon substrates are bonded together with a silicon oxide film interposed therebetween; ELTRAN (registered trademark) technology in which selective etching of a porous silicon layer is used; and the like have been disclosed.
Of these technologies, bonding SOI technology has been attracting attention because therewith an SOI layer with high crystallinity can easily be formed over substrates other than silicon substrates (quartz substrates, ceramic substrates, and the like, for example). However, in fabrication of a bonding SOI substrate, there are problems in that deterioration in quality due to contamination of the SOI layer, warping of the substrate, and the like occur, which adversely affects device characteristics.
Thus, for solving these kinds of problems, technology for fabrication of bonding SOI substrates, by which two wafers are directly bonded together, has been proposed (for example, in Patent Document 1: Japanese Published Patent Application No. 2004-320050). In Patent Document 1, a method of fabricating an SOI substrate has been disclosed, in which, after a substrate in which a silicon oxide layer, a silicon nitride layer, and a polycrystalline silicon layer are stacked over a single-crystal silicon layer in the order given, and a support substrate, which is provided separately, are washed with a solution and the surface of each of the substrate and the support substrate is activated; the two wafers are directly bonded to each other; and heat treatment is performed to bond the substrate and the support substrate together so that an SOI substrate is formed by grinding and polishing of the single-crystal silicon film that is to be an active layer.